The object of the present invention is the development of a fluidized bed reactor for the working up of carbon coated nuclear fuel and fertile material particles for nuclear reactors consisting essentially of a cylindrical portion and a conical portion with gas supply lines, gas distribution space and gas distribution heads.
In the nuclear art, there are used spherical particles as nuclear fuel or fertile material. These particles have a heavy metal containing nucleus of uranium and/or thorium compounds, e.g., uranium carbide or uranium oxide or thorium oxide or thorium carbide. This heavy metal nucleus for physical reactor reasons (among others) coated with carbon. In the working up, e.g., for return of these particles to production therefore the carbon coating must first be removed before the exposed heavy metal nucleus can again be worked up.
The removal of the carbon coating normally takes place by burning where the heavy metal nuclei freed from their coating are present with reduced diameter and with high density as "Combustion Residue" for further working up. In this connection, it is important for the further working up that the carbon coating be completely burned off. Above all, this can be attained by the use of known fluidized bed principles in fluidized bed reactors. The burning of the carbon layer thereby must take place from the view of nuclear criticality safety.
The use of fluidized bed reactors for chemical processes is generally known (e.g., Chemie-Anlagen und-Verfahren, February 1972, pages 51-53). Typical of these fluidized bed reactors is a lateral discharge of material or a discharge of material by means of overflow. There is also known the possibility of withdrawing the material through a pipe vertically through the blower bottom foreign to the discharge of material (J. Beranek et al, Grundlagen der Wirbelschichttechnik, page 198, Mainz 1975).
In comparison to the coated particles, the uncoated particles are specifically heavier and therethrough at a specific speed of flow out of the fluidized bed reaction corresponding to the advancing coating removal sediment vertically downward the burned off heavy metal nuclei can only be incompletely drawn off through lateral discharge of material of through the discharge by means of an overflow. This is disadvantageous, e.g., because of the criticality and the nuclear fuel balance. Even if the heavy metal nuclei are discharged by a pipe, a complete withdrawal is only attainable below the flow injuring construction of the blower bottom.
Therefore, it would be advantageous to use a fluidized bed reactor in which there is possible a downward discharge of burned off particles even at a reactor diameter greater than 800 mm and in which no material temperature can occur above 650.degree. C. Such a reactor which fulfills these conditions has not been previously known.
Therefore, it was the problem of the present invention to construct a fluidized bed reactor for working up carbon coated particles, particularly nuclear fuel particles or fertile particles which permitted a downward discharge of burned off heavy metal particles even at large reactor diameters, so that practically the entire reactor content gradually can be drawn off without the flow ratios required to maintain the fluidized bed being negatively influenced and particles sintered together through too high material temperatures at the bottom of the reactor.